The base is original from the producer (chords and melodies), but is complemented with elements that complement the song that come from samplepacks, usually, vocal chops, guitars, wobbles sections, glitch effects. It is the standard in which most of producers work, in a project you will find MIDI files made by the producer, but also melodic loops.
Project is well organised if change is needed.
Sample pack Vandalism - Ultra Chillout Guitars
Loop name Ultra_Chillout_Guitars_02_128_BPM_G